1. The exponential power distribution method could be speeded up by
using a rational function approximation for the rejection scaling
parameter.

x2. Check for off by one error in the shuffle algorithm. DONE. checked
against Knuth.

x3. If the user runs gsl-dist for two different distributions then the
variates will be correlated because they come from the same stream of
random numbers. DONE, the user now has to supply a seed

4. Do something about the possibility of the user providing invalid
parameters (e.g. negative variance etc)

5. Add the triangular distribution.

x6. Add the Rayleigh distribution. DONE
